The mammary gland is a complex organ which is under a myriad of regulatory controls. These include circulating hormones and growth factors, as well as local trophic factors produced by the mammary epithelial cells (MEG) or by the stroma within which the MEC are embedded. In addition, the components of the extracellular matrix (ECM) have been found to exert a profound effect on both the morphological and functional development of the mammary gland. The objective of the studies proposed herein is to investigate the mechanism by which the ECM exerts its effect on morphological and functional differentiation of the mammary gland, with specific emphasis on the interaction of ECM proteins with their cellular receptors (integrins and non integrins), and the mechanism by which this interaction alters cytoskeletal remodeling and thus milk protein gene expression. The overall goal of these studies is to determine the mechanism by which communication between the extracellular and intracellular matrices directs gene expression in normal cells, and to determine the mechanism(s) by which this regulation is disrupted in malignant cells. AIM 1. To study the role of the ECM in regulating the proliferation and differentiation of normal rat MEC (RMEC). This aim will focus on the effect of agents which disrupt the binding of fibronectin and laminin to their cellular receptors (with emphasis on the alpha5beta1 and alpha6beta4 integrins and the non integrin 32/67 kDa laminin receptor [LR]), with the goal of determining the importance of each of these receptors on cellular function. AIM 2. To determine the mechanism by which the ECM proteins laminin and fibronectin stimulate morphological and functional differentiation of RMEG. This aim will focus on the cytoskeletal changes that occur in response to binding of laminin or fibronectin to their receptors, or in response to disruption of this interaction, and assess whether TGF and/or protein tyrosine phosphorylation (especially of the actin attachment protein vinculin) are essential mediators of this signal transduction pathway. AIM 3. To investigate the regulation of integrin expression of normal RMEC. The integrin family of cell surface receptors are critical components in the pathway by which EGM proteins modulate proliferation and differentiation. In order to determine if changes in integrin expression and/or activity can modify EGM signalling, the functional significance of changes in expression will be assessed in normal RMEG, with focus on the integrins alpha5beta1 and alpha6beta4, as well as on LR AIM 4. To investigate the role of protein kinase C (PKC) (PKC) in modulating the response of normal RMEC to EGM proteins. In this aim, the effect of phorbol esters on (i) cytoskeletal redistribution of specific PKC isoenzymes and (ii) on the interaction of the RMEG with the EGM will be assessed, with the goal of determining whether a PKC-mediated phosphorylaUon event is required for a functional ECM-cellular interaction. AIM 5. To compare regulation of integrin and LR expression and function in normal and transformed MEC. The goal of these studies is to assess the importance of the integrins alpha5beta1 and alpha6beta4 and the non integrin LR in regulating the interaction of the cells with their ECM as well as to probe the significance of these proteins in altering the tumorigenic and metastatic potential of mammary tumor cells.